The present invention relates to snowmobiles, and more particularly to snowmobiles with engines having air chargers such as exhaust-driven (turbo) or mechanical superchargers.
Conventionally, snowmobiles have been made small and light weight, yet have relatively powerful engines in order to appeal to the typical snowmobile driver. Because of the small size, the packaging of the components in a snowmobile is critical. However, due to its sporting nature, it is also desirable to have a snowmobile that is powered by an engine that is not only efficient and light weight, but also generates significant power for its size. So, traditionally, two cycle engines have been used to power snowmobiles. These engines have the advantage that they are powerful, yet relatively light weight and compact. One particular disadvantage to the two cycle engine is its emissions—it generally exhausts more hydrocarbons and other pollutants than an equivalent four cycle engine due to cylinder charging inefficiencies and the combustion of lubricating oil, among other things. Also, the two cycle engine tends to operate at a relatively high noise level. With concern for the environment and increasing strict emissions requirements being instituted by governments, it is increasingly desirable to use four cycle engines with snowmobiles.
But a naturally aspirated four cycle engine generally produces less specific output per liter of engine displacement than does a two cycle engine. It is not practical to merely increase the engine size due to the size and weight limitations present in packaging an engine in a snowmobile. Furthermore, the typical transmission employed in a snowmobile limits the upper end of the RPM range for the engine. To increase the output of a particular four cycle engine, then, one may wish to employ an air charging system, such as a turbocharger (exhaust driven compressor) or a supercharger (mechanically driven compressor). However, a conventional air charger will require the use of a higher grade of gasoline in order to avoid detonation and pre-ignition problems (i.e. engine knock), which can over time significantly reduce the useful life of an engine. This higher grade of gasoline is not always available to a snowmobile driver along the various trails that he may travel.
Thus, it is desirable to have a snowmobile that is powered by a four cycle engine which overcomes the drawbacks of limited engine output, while still remaining relatively small and light weight. In particular, it is desirable to have an air charging system that maximizes the engine output while not requiring a premium grade of gasoline.